The present invention generally relates to liquid-cooled heat sinks, and more particularly to a liquid-cooled heat sink for electronic devices that includes obstructions for optimizing heat transfer to the stream of liquid and which includes a thermal jacket to prevent surface moisture condensation from forming during subambient operation.
The performance of electronic circuits and their semiconductor devices is limited by temperature. Semiconductor device performance degrades when the internal temperature reaches or exceeds a particular limit. That limit depends upon the nature of the semiconductor device. In order to maintain or increase the performance of such devices, they must be cooled in some way. The manner of cooling depends upon many parameters, including the space available for the cooling process, the temperatures to be encountered, power, etc. In some instances simply passing a fluid over the device or, over a finned heat sink that is attached to the device, is sufficient to maintain the semiconductor at safe operating temperatures.
In one known semiconductor device cooling technique, convecting fins are attached to a semiconductor package, or the package is affixed to a larger metal member, referred to as a heat sink or cold plate. This heat sink draws heat away from the semiconductor device and can be air cooled or liquid cooled, depending upon the particular application. If the heat sink is air cooled it will typically have heat convecting fins.
Different cooling fluids may be used, when liquid cooled methods are employed, depending upon the application and the density of the electronic devices in a given circuit. Boiling liquids are often used, such as fluorinated hydrocarbon refrigerants, which are delivered to the cold plate in liquid form and are boiled to remove heat. These systems often have the highest heat removal rate for a limited xe2x80x9ccold platexe2x80x9d area, but require a considerable amount of power to operate, i.e. to be pumped to and from the heat transfer site. In other systems, a cold liquid is circulated through the cold plate with the cold liquid being refrigerator cooled, evaporatively cooled, or convectively cooled.
A problem exists in the foregoing prior art systems in that a portion of the liquid used to cool the semiconductor device tends to stagnate in a region close to the surface of the heat sink. This stagnation typically refers to a reduction in coolant speed near the heat sink surface. Here the coolant flows at a slower than required speed to adequately remove heat from the heat sink surface. This stagnation reduces the effectiveness of the heat transfer in the cooling system. Very often, the rate of cooling is less than the rate at which heat arrives at that interface surface, which causes an accumulation of heat at the surface. Several options have been proposed in the art to reduce this effect, including increasing the speed of the flow of the coolant or introducing structural features which cause turbulent flow and increased effective surface area.
Under certain circumstances, moisture from the ambient environment may condense on the heat sink or cold plate. In the case of liquid-cooled heat sinks, there are periods of time during which the temperature of the heat sink may fall below the temperature of the surrounding environment, often referred to in the art as xe2x80x9csubambientxe2x80x9d operation. This condition may occur any time the surface temperature of the heat sink falls below the ambient temperature. When this subambient operation condition occurs, moisture from the surrounding atmosphere may condense on the outer surface of the heat sink. The condensed moisture collects and runs off of the heat sink and into contact with the circuit board, semiconductors and packages, and other components. This free liquid can cause significant damage to those components and degrade the overall performance of the electronic device, or even destroy it all together.
There is a need for a liquid-cooled heat sink having a thermal jacket that can be positioned on or near a semiconductor package that will provide both optimum turbulent flow and increased surface area for effective heat transfer to the stream of liquid, and reduce or prevent condensation from forming in appreciable quantities on the surface of the device during subambient operation.
A liquid-cooled heat sink having a thermal jacket is provided including a housing with a peripheral side wall extending from the perimeter of a bottom wall and a lid sized to engage the peripheral side wall so as to form a chamber. A fluid inlet port and a fluid outlet port are defined through the lid, and disposed in fluid communication with the chamber. A plurality of pins project outwardly from the bottom wall so as to be positioned within the chamber and arranged in a staggered pattern. The pins include an end that engages the lid to provide structural support, and to prevent deflection of the lid by high liquid pressure. The liquid cooled heat sink of the present invention also includes a thermal jacket that reduces the rate of condensation of moisture during subambient operation of the liquid-cooled heat sink. The thermal jacket includes a bonding layer positioned in substantially surrounding and overlying relation to the liquid-cooled heat sink, at least one porous layer positioned in substantially surrounding and overlying relation to the bonding layer, a barrier layer positioned in substantially surrounding and overlying relation to the at least one porous layer; and a sealant layer positioned in substantially surrounding and overlying relation to the barrier layer. In this way, the at least one porous layer traps air close to the surface of the heat sink so as to provide a thermally insulating air barrier between the surface of the heat sink and the ambient environment.
In one alternative embodiment of the invention, a liquid-cooled heat sink is provided having a housing including a peripheral side wall extending from the perimeter of a bottom wall and a lid sized to engage the peripheral side wall so as to form a chamber. A fluid inlet port and a fluid outlet port are defined through the lid, and disposed in fluid communication with the chamber. A fin having a plurality of corrugations is positioned within the chamber so that at least one of the corrugations engages the bottom wall and at least one of the corrugations engages the under surface of the lid. A thermal jacket is formed on the outer surface of the heat liquid-cooled sink that includes a bonding layer positioned in substantially surrounding and overlying relation to the cooled heat sink, at least one porous layer positioned in substantially surrounding and overlying relation to the bonding layer, a barrier layer positioned in substantially surrounding and overlying relation to the at least one porous layer; and a sealant layer positioned in substantially surrounding and overlying relation to the barrier layer. Here again, the at least one porous layer traps air close to the surface of the heat sink so as to provide a thermally insulating air barrier between the surface of the heat sink and the ambient environment.